Current available broadcasting services have various types. Such types of broadcasting services have been advanced from an analog type broadcasting service to a digital type broadcasting service. The digital type broadcasting service provides high quality broadcasting services with diverse audiovisual information. Hereinafter, the analog type broadcasting service and the digital type broadcasting service will be described.
Conventional analog type broadcasting uses a multiple frequency network (MFN) in shadow areas of a broadcasting station and a secondary station in order to prevent same frequency interference. The MFN changes a channel using frequencies different from a central frequency to provide a broadcasting service. Since the MFN allocates different frequency to each service to provide broadcasting services, no channel interference occurs. Accordingly, the MFN may be an ideal network for providing a broadcasting service if frequency resources are not limited. However, it is difficult to use the MFN due to limitation of available frequency resources. In order to overcome the shortcoming of the MFN, single frequency network (SFN) was introduced for effectively using the limited frequency resources. The SFN also has a shortcoming that the SFN cannot be used for analog type broadcasting due to interference caused by using the same frequency. However, the SFN can be used for the digital broadcasting system.
An Orthogonal Frequency Division Multiplexing (OFDM) scheme and a Vestigial Side Band (VSB) scheme introduced by the Advanced Television System Committee (ATSC) are representative schemes of a digital broadcasting system.
In order to support the SFN, the digital broadcasting system should employ the OFDM scheme. The OFDM scheme divides data sequence, which is transferred using one carrier, into a plurality of data sequences using a plurality of subcarriers having orthogonality and transmits the plurality of data sequences at the same time. The OFDM scheme inserts a guide interval to prevent orthogonal component from scattering due to intersymbol interference. Here, the intersymbol interference is caused due to delay during transmission. Also, the OFDM scheme improves receipt capability by enabling a receiver to recognize a plurality of signals as a multipath signal. That is, the OFDM scheme provides a better SFN environment.
The U.S. employs the VSB scheme as a transmission method. The VSB scheme transmits high quality video, audio, and additional data using single 6 MHz bandwidth and supports two broadcasting modes, a terrestrial broadcasting mode and a high-speed data broadcasting mode. Particularly, the VSB scheme symbolizes a digital signal and performs VSB modulation like a conventional analog VSB scheme and uses an 8-VSB scheme for the terrestrial broadcasting mode.
In the SFN environment, performance may be deteriorated due to the interference that is caused by signals of adjacent transmitters. In order to overcome the problem, a transmitter identification (TxID) technology was introduced. The TxID technology assigns a unique ID to each transmitter or each repeater and signals from transmitters or repeaters are identified based on the transmitter identification TxID. The transmitter identification may be inserted as a parameter-like transmitter identification information (TII), which is defined in DAB of Eureka 147 or T-DMB of South Korea. Alternatively, the transmitter identification may be inserted into a data symbol in a form of a watermark in spread frequency spectrum, which is defined in TxID of ATSC. A general receiver cannot identify the transmitter identification TxID. The transmitter identification TxID is identified by a specific receiver and used for special purpose such as network design or channel estimation. Since the transmitter identification TxID is one of representative digital data, the transmitter identification TxID will be described as digital data.
Hereinafter, an apparatus for inserting digital data according to the prior art will be described with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a typical OFDM system of a DVB-T transmitter.
As shown in FIG. 1, the OFDM transmitter includes a multiplexing (MUX) adapter 101, an external and internal coder 102, an interleaver 103, a data mapper 104, a frame adapter 105, an OFDM modulator 106, a guard interval inserter 107, a digital-to-analog converter (DAC) 108, an RF up-converter 109, a high power amplifier (HPA) 110, and a pilot and transmission parameter signal (TPS) carrier inserter 111.
The operation of the typical OFDM modulation system of a DVB-T transmitter will be described.
In the typical OFDM modulation system of the DVB-T transmitter, the multiplexing adapter 101 receives a transport stream (TS) packet through a link and multiplexes the received TS packet. The external and internal coder 102 receives and encodes the multiplexed TS packet from the multiplexing adapter 101. The interleaver 103 rearranges the coded TS packet from the external and internal coder 102 to prevent consecutive error, that is, burst error. The data mapper 104 maps data. The frame adaptor 105 receives the mapped data and generates a frame in a format that is required by a corresponding network to transmit. The pilot and TPS carrier inserter 111 inserts a pilot symbol and a TPS carrier into the frame. The OFDM modulator 106 modulates the frame from the frame adaptor 105 through OFDM modulation, and the guard interval inserter 107 inserts a guard interval to prevent orthogonality from scattering due to the delay of subcarriers. The digital-to-analog converter 108 converts a digital signal to an analog signal to transmit the modulated packet to the RF up-converter 109 in order to transmit the modulated packet using wireless medium. Then, the digital-to-analog converter 108 transmits the converted packet to the RF up-converter 109. The RF up-converter 109 converts frequency to a frequency band that a system uses. The high power amplifier 110 amplifies the output of the signal according to a transmitter and transmits the signal to the antenna. The antenna transmits the signal.
FIG. 2 is a diagram illustrating an ATSC VSB transmitter according to the prior art.
Referring to FIG. 2, the conventional VSB transmitter includes a data randomizer 201, an RS coder 202, an interleaver 203, a trellis coder 204, a TxID inserter 205, a multiplexer (MUX) 206, a pilot inserter 207, a VSB modulator 208, an RF up-converter 209, and a high power amplifier 210.
The operation of the typical ATSC VSB transmitter will be described with reference to FIG. 2.
The data randomizer 201 arranges the TS packet to be usable in a corresponding system. The RS coder 202 inserts an RS code for error correction. The interleaver 203 regularly rearranges the RS code inserted packet to prevent burst error and to protect data. The trellis coder 204 generates 8-level (3-bit) trellis code for VSB modulation. The TxID inserter 205 inserts a transmitter identification to the trellis coded data. Although the ATSC VSB transmitter of FIG. 2 includes the TxID inserter in front of the multiplexer, the TxID inserter can be disposed behind the multiplexer. For convenience, the TxID inserter will be described as disposing in front of the multiplexer.
The multiplexer 206 performs multiplexing based on segment synchronization and frame synchronization. The pilot inserter 207 inserts a pilot signal into each frame and transmits the pilot inserted signal to the VSB modulator 208. The VSB modulator 208 receives the 8-level trellis coded signal with TxID inserted, the pilot signal, the frame and segment synchronized signal and modulates the received signals based on VSB modulation. The RF up-converter 209 converts the VSB modulated data to a radio frequency (RF) and transfers the RF to the high power amplifier 210. The high power amplifier 210 increases the output and transmits the amplified signal through an antenna.
FIG. 3 is a diagram illustrating a TxID signal generator and an injection level controller for inserting a transmitter ID (TxID).
Referring to FIG. 3, a transmitter ID (TxID) of a typical ATSC transmitting and relaying device is inserted between the trellis coder 303 and the VSB modulator 304. A TxID signal generator 301, which is a 2-level kasami sequence generator, generates the transmitter ID (TxID), and an injection level controller 302 controls a size of the transmitter identification TxID suitable to the size of a 8-VBS symbol and adds the size controlled transmitter identification TxID into the symbol. The TxID inserted signal is additionally inserted into the original trellis coded symbol and is controlled not to significantly influence the original signal. The VSB modulator 304 receives the transmitter identification TxID and the 8-VSB signal and performs the VSB modulation thereon.
FIG. 4 is a signal level graph showing a level difference between an 8-VSB signal and a TxID signal.
In FIG. 4, a curve 401 indicates a signal level of an 8-VSB signal and a curve 402 represents a signal level of additional information inserted by a broadcasting system. The two signals 401 and 402 are realized to have a level difference of about 21 to 39 dB. The reason of realizing the two signals to have the predetermined level difference is to add the additional information in the 8-VSB signal 401 as noise by inserting the transmitter identification TxID signal 402 in a small size and not to significantly influence the 8-VSB signal 401.
As described above, it is required to arrange the transmitter identification TxID inserter between the trellis coder 204 and the VSB modulator 208 for a broadcasting system to transmit the transmitter ID (TxID). However, the trellis coder 204 and the VSB modulator 208 have been integrally formed as a chip or a board in a transmitter or a repeater. Accordingly, in order to transmit the TxID, it is necessary to replace a related chip or board. Replacing the entire chip or board is very wasteful in view of economy and human resource. In case of replacing equipment due to characteristics of a broadcasting service, it is required to replace all of transmitter and repeaters in entire area. Accordingly, replacing equipment in entire area is impossible and very difficult task. Furthermore, replacing a predetermined part of system may cause incompatibility problem with existing systems.